The third important aspect of the sound wave is the waveform or shape of the sound wave. This determines the timbre or quality of the sound, and it enables us to tell the difference between a trumpet and a guitar, even if both instruments are producing a tone of the same frequency and amplitude.

For example, plucking one of the guitar’s strings causes the string to vibrate at a particular frequency. But the string's vibration also causes each piece of wood in the guitar to vibrate at a frequency related to that piece's length and thickness. These different frequencies are merged into the sound wave produced by the guitar string. The resulting complex wave is the guitar’s signature; our ears can tell that the sound was made by a guitar rather than by a trumpet or piano.

On the next page test your ears by listening to each of these “mystery instruments” play the same note, and then try to guess the name of each instrument. To check your guesses, select the “Identify the Instruments” button.